To form a semiconductor device, contacts or other openings, for example in an oxide, are often formed to expose an underlying layer such as a wafer, a metal layer, a polycrystalline silicon layer, or various other layers. To protect a desirable layer such as a word line or a digit line over the layer to be exposed, an etch stop layer or a sacrificial layer is formed over the desirable layer. The sacrificial layer often comprises silicon nitride. During the removal of an oxide layer, the silicon nitride etch stop layer can also be removed albeit usually at a slower rate than the oxide removal. The erosion of the silicon nitride layer can cause problems, for example if the underlying layer is exposed and erosion begins on the underlying layer.
A process sequence which protects a desired layer more efficiently than previous process sequences would be advantageous.